1. Technical Field of the Invention
The present invention relates generally to solenoid switches or electromagnetic switches. More particularly, the invention relates to a solenoid switch for an engine starter, which includes a moving contact configured to prevent contact bounce from occurring during operation of the solenoid switch.
2. Description of the Related Art
There is known a solenoid switch for closing and opening a motor circuit of an engine starter. The solenoid switch includes a pair of fixed contacts, which are included in the motor circuit as main contacts, a moving contact working to connect and disconnect the fixed contacts, and a solenoid working to actuate the moving contact.
In such a solenoid switch, when the moving contact is moved by the solenoid to strike the fixed contacts, the moving contact will bounce in the opposite direction to the striking due to the reaction force of the fixed contacts. The striking and bouncing may repeat several times until establishment of a stable contact between the moving contact and the fixed contacts, thus causing the so-called contact bounce. As a consequence, the moving and fixed contacts may be quickly worn down due to large-current arc discharge, and in the worst case, they may be welded to adhere together.
To suppress occurrence of contact bounce, Japanese Patent First Publication No. 2001-107828 discloses a first approach, according to which the attracted motion of a plunger is slowed down by an air-damping effect, thereby reducing the impact load generated during the striking of the moving contact against the fixed contacts.
However, with the first approach, it is difficult to reliably suppress occurrence of contact bounce when the solenoid switch is used for an automotive engine starter. More specifically, the temperature in an automobile generally changes largely, and the air-damping effect depends on the temperature. Accordingly, it is difficult to secure the stability of the air-damping effect.
For the same purpose, Japanese Patent First Publication No. H09-161639 discloses a second approach, according to which the center of gravity of the moving contact and the center of gravity of a contact pressure spring are oppositely deviated from a center line, thereby producing an angular moment to damp the movement of the moving contact.
However, with the second approach, it is still difficult to reliably suppress occurrence of contact bounce when the solenoid switch is used for an automotive engine starter. More specially, there are often produced high vibrations in an automobile, and thus the behavior of the moving contact and the contact pressure spring, the centers of gravity of which are oppositely deviated, tends to become unstable. Accordingly, it is difficult to reliably damp the movement of the moving contact.